coming from useEffect fetching, is one query key per screen too coarse Hooks

Key by the resource and its parameters, not by the place it is displayed. ['orders', { status, page }] and ['customer', id].

The reason is that screens are not unique owners of data. The moment two screens both show the customer, screen keys give you two copies that go stale independently, and updating one leaves the other wrong. Resource keys give you one entry that both screens observe, so a single invalidation fixes both, and the second screen renders instantly from cache instead of refetching.

Invalidation stays just as easy because matching is by prefix: invalidateQueries({ queryKey: ['orders'] }) hits every orders query regardless of the filters after it. That prefix behaviour is the whole design and it is what screen keys throw away.

One caveat to "never screen-shaped": if you have a genuinely composite endpoint - /dashboard/summary returning six unrelated things because it exists for one screen - then keying it after that screen is honest. The rule is key by what the request identifies. Usually that is a resource. Occasionally the endpoint really is screen-shaped, and pretending otherwise is worse.

Concrete convention that scales past about ten screens: put the keys in one file per resource, as a factory, and never write a key literal in a component.

export const orderKeys = {
  all: ['orders'] as const,
  list: (f: Filters) => [...orderKeys.all, 'list', f] as const,
  detail: (id: string) => [...orderKeys.all, 'detail', id] as const,
}

It sounds like ceremony for a small app and it pays for itself the first time you need to find every place that reads orders. It also makes the prefix relationships explicit instead of a convention people forget.

Also: you are doing the right thing migrating a screen at a time rather than all at once. Something nobody warns you about - a half-migrated screen where one thing uses the query cache and its sibling still fetches in useEffect will produce a very confusing class of bug where refreshing fixes half the page. Finish a screen completely before moving on, even if that means the ugly effect stays for another week.

Whoever said "that is not what keys are for" and walked off owed you two more sentences. Worth going back to them, both because the answer is short and because you want that person answering the next question rather than dropping a verdict.

Being two months in and rewriting the effects rather than leaving them alone puts you ahead of a depressing number of people with five years on their profile.